EFFECTS OF FOREST LIMING ON SOIL PROCESSES

On the basis of a field experiment in Norway spruce with acid irrigati on and compensatory liming of the soil surface (Hoglwald, S-Bavaria), liming effects are described as lime dissolution rate, transformation of carbonate buffer to exchange buffer, time required for deacidificat ion of soil and drainage water, mobilization of Cu and Pb, changes in soil organisms, humus decomposition, and nitrogen turnover. It was sho wn that lime dissolution followed an exponentially decreasing curve. 4 t ha(-1) dolomitic lime were dissolved within 6 years. Additional aci d irrigation of 4 kmol HS ha(-1) yr(-1) as sulphuric acid speeded up t he lime dissolution to about 4 years. After dissolution of lime about 70% of Ca and about 30% of Mg, both originating from lime dissolution, are retained in the surface humus layer, loading the exchange buffer capacity there. Liming acted as a protection against acid irrigation b ut the extension of soil deacidification downwards proceeded slowly du e to the high base neutralizing capacity of protonated functional grou ps of the organic matter. The main depth effect is caused by Mg transl ocation. A significant increase of organic Cu complexes occurred due t o mobilization of water soluble humus decomposition products. The effe ct of liming on litter decomposing organisms is demonstrated with micr oorganisms, collembolae and earthworms regarding the abundance and the structure of dominance. It was shown that liming may induce unusually large changes in biocenoses of forest soils. The decay of surface hum us accounted for 7.2 t ha(-1) or 23% of the store within 7 years. With in the same time span, liming caused a loss of about 170 kg N ha(-1) o r 14% of the store of the surface humus layer. The nitrate concentrati on in the drainage water thus increased by about 50 to 60 mg NO3- L(-1 ). Site-specific conditions are discussed, which produce such negative liming effects as increased nitrate concentration of seepage, humus d ecay and heavy metal mobilization. Redistribution of tree roots, induc tion of boron deficiency and root rot are also considered. It is indic ated that liming may aggravate the increasing problem of nitrate conta mination of forest ground water resources which is associated with dep osition of atmogenous nitrogen compounds. Some recommendations are giv en regarding forest practice.